AIM 

To investigate the influence of cast immobilization after ankle injury on the biomechanical properties of the Tibialis Anterior (TA) muscle-joint-tendon complex (TAMJTC) by the esteem of its transfer function (TF) parameters.

METHODS 

Control group (5males and 3 female: age 29±7.5 yo), ankle injured group (10 males and 3 females: age 28.6±8.4 yo). The electrically evoked TA torque was detected by an isometric ergometer with a load-cell linked to the foot sole. The amplitude of a 40 Hz stimulation train administered to the TA motor point was varied sinusoidally with at (0.4, 1.0, 1.8, 2.5, 3.0, 4.5, 6.0 Hz; total duration of ~12 s). From the each subject Bode plots for gain attenuation and phase shift at each modulating frequency, with respect to the input sine, the model parameters were calculated.

RESULTS AND COMMENTS 

In both groups it was possible to model the TAMJTC force dynamic response by a critically damped II order system with two coincident poles + a pure time delay:

- control group: poles at 2.63 (±0.46) Hz and pure time delay of 16.3 (±3.7) ms.

- patients group: poles at 2.19 (±0.30) Hz and pure time delay of 20.53 (±8.99.1) ms.

Only the poles position (Hz) in the injured subjects group was significantly different from controls (P<0.05). The quantification of the muscle-tendon unit frequency response discloses the influence of the immobilisation on the visco-elastic properties of the TAMJTC inducing changes toward a slower system having a decreased stiffness possibly related to functional ankle instability.